The present invention relates to a method of fabricating semiconductor structures, and more particularly to a method of improving the material quality near the surface of a defective semiconductor crystal.
In current semiconductor technology, strained-silicon-on-insulator (SSOI) substrates are being considered for use in high-performance complementary metal oxide semiconductor (CMOS) device technology due to the improved charge carrier mobilities in strained-silicon-on-insulator substrates as compared to unstrained Si-on-insulator starting substrates (i.e., SOI).
Low defect density SiGe-on-insulator (SGOI) material is currently produced by one of two methods: 1) growth of a relaxed silicon germanium (SiGe) alloy layer on a bulk Si substrate and layer transfer of the relaxed SiGe alloy layer onto an oxidized xe2x80x9chandlexe2x80x9d substrate; or 2) growth of a strained SiGe alloy layer on an existing SOI substrate followed by high temperature annealing to homogenize and relax the SiGe alloy layer over the oxide layer.
After the SiGe-on-insulator (SGOI) has been formed, a layer of Si is grown epitaxially to make the strained silicon layer (tensile strain). Even with low defect SGOI, it is possible to create defects within the strained Si layer as a result of direct Si growth on the SiGe template. For strained silicon layers to be useful for modern CMOS integrated circuit (IC) technology, the number of defects within the electrically active regions of the material must be kept to a minimum.
To date, there is no prior art that is concerned with improving the material quality near the surface of defective semiconductor crystal materials such as SSOI substrates. The present invention provides a method whereby the material quality of a defective semiconductor material crystal is improved.
An object of the present invention is to provide a method for improving the near surface quality of a previous defective semiconductor crystal.
Another object of the present invention is to provide a method of improving the quality of a defective semiconductor crystal material that is simple, cost effective and is compatible with conventional CMOS processing.
A further object of the present invention is to provide a method of improving the quality of a defective bulk or heterostructure semiconductor crystal material.
These and other objects and advantages are achieved in the present invention by utilizing a method in which a defective semiconductor crystal material is subjected to an amorphization step followed by a thermal treatment step. In accordance with the present invention, the amorphization step amorphizes, partially or completely, a region, including the surface region, of a defective semiconductor crystal material. A thermal treatment step is next performed so as to recrystallize the amorphized region of the defective semiconductor crystal material. Specifically, the recrystallization is achieved in the present invention by solid-phase crystal regrowth from the non-amorphized region of the defective semiconductor crystal material.
The solid-state regrowth translates only those defects that extend past the amorphous layer and thus eliminates any Si (or other epitaxial layer) growth-related defects. As long as the semiconductor crystal material, for example Si/SiGe heterostructure, is thermodynamically stable with respect to strain-relieving defect production, the amorphized semiconductor crystal material will recrystallize with the same magnitude of strain without the introduction of additional defects. In the present invention, solid-phase recrystallization will occur as long as the amorphous region does not extend to a buried amorphous layer (e.g., a buried oxide layer) within the semiconductor crystal material or entirely through the semiconductor crystal material. In bulk strained-Si technology, layers will regrow with the defect density defined by the material quality at the amorphous/single crystal interface.
In broad terms, the method of the present invention comprises the steps of:
amorphizing, partially or completely, a region of a defective semiconductor crystal material; and
thermally treating the amorphized defective semiconductor crystal material to recrystallize said partially or completely amorphized region forming a recrystallized region that has a reduced defect density as compared to the defective semiconductor crystal material.